15. Yeah,but they have to be close by the plants...
...which would be out in the middle of nowhere turning wind and solar into gasoline on land that's not being used otherwise.
I'm not saying they couldn't be built, but it would be much faster to simply use the existing road network and keep the deliveries local. Maybe each plant built could supply all the gas stations within 100 miles, and that would be performed by a few tanker trucks making regular runs.
A distributed network of conversion plants across the Midwest and Southwest could ultimately supply 100 million people with automotive fuel, cutting our fossil fuel consumption by a significant portion.